Effects of High Doses of Iodide on Thyroid Secretion: Evidence for the Presence of Iodinated Membrane Tubulin

The transient inhibitory effect on thyroid secretion produced by high doses of iodide was investigated with respect to changes in the level of in vivo iodination of membrane tubulin. Iodinated tubulin, characterized by gel electrophoresis, immunoprecipitation, and peptide mapping, was shown to be associated with a thyroid membrane fraction, and totally absent from cytoplasmic proteins. The administration of an acute dose of 5 mg KI, although it inhibited thyroid secretion (as shown by an increase in TSH), did not have a significant effect on the level of iodination of membrane tubulin. Thus, the observed inhibition of thyroid secretion is probably unrelated to the level of iodination of tubulin. Although its function is not known at present, iodinated tubulin is probably involved in membranerelated phenomena. (Endocrinology 117: 607–612, 1985)